The use of electromagnetic beams in ellipsometer and the like systems, wherein a single Angle-of-Incidence (AOI) and Plane-of Incidence (POI) of the beam to a sample surface under investigation, (that typically being the (AOI) and (POI) of a Central Beam Ray), is applied in characterizing the sample, is known. This is sufficient in many settings, however, decreasing sample size, increasing demand for measured parameter accuracy and increased information content in beams has led to measurement systems becoming more complex. In newer systems each part of a measurement beam no longer produces equivalent results when compared to other parts. In measurement systems where different parts of a measurement beam produce different sample characterizing data, a single data set representative of the natural addition (or convolution) of these different data sets (from each part of the beam) is produced. And, when this single data set deviates enough from a data set taken with a uniform beam at a single (AOI) and (POI), then a more detailed System calibration and data Analysis procedure is needed that takes into account the different optical paths that each part of the measurement beam experiences. Various parts of a sample investigating beam can produce different results because of different reflection, refraction, coordinate System changes, (AOI), (POI) and general polarization state changes, as well as source beam uniformity, aperture effects and variable attenuation effects. These effects are referred to as Multi beam-ray effects (MBRE) herein. In some cases Multi beam-ray effects are small or trivial such as those that cause simple (AOI) smearing. The Present Invention is concerned with non-trivial Multi beam-ray effects but is also applicable to the trivial cases if desired. The present invention provides particular Utility where some or all of the 16 sample Mueller Matrix elements are used to derive sample Parameters, while in some cases the Mueller Matrix elements themselves are the Parameters of interest.
Results from ellipsometer or the like Systems that experience significant Multi beam-ray effects are improved by application of the present Invention, which seeks to overcome the problems as listed above by subdividing the measurement beam into a certain set of beam-rays. The proposed method includes providing parameterized mathematical models for each beam-ray that takes into account the various multi beam-ray effects, and determining Sample Mathematical model Parameter values in a data Regression calibration step that includes convoluting said parameterized mathematical model. A sample investigation system characterized in a way directed by the present invention is then used to Analyze data from an unknown, (hereafter “sample”), sample to determine Parameter values thereof which are free from considered Multi beam-ray effects and which deviate less from theoretical “true” values than would have been obtained from a “single ray” ellipsometer or the like System.
A known Patent of interest is U.S. Pat. No. 7,671,989 to Liphardt et al. This Patent describes preserving information in a beam of electromagnetic radiation by, when utilized, apertures to, for instance reduce beam size, are applied so as to preserve the angle-of-incidence (AOI) at which the beam is directed toward a sample. That is, equal amounts of beam are interrupted at top, bottom, left and right locations. The beam involved is considered to be a single beam. Another known reference is Published Patent Application No. 2011/0246141 by Li. This reference discloses modeling a beam of electromagnetic radiation as a plurality of rays, and applying said beam to a diffraction grating, (ie. a “structured” sample), which is fabricated in close proximity to a workpiece, such as a wafer, photomask or magnetic medium. For emphasis, Li 141 teaches that the beam of electromagnetic radiation involved is caused to diffract off a periodic structure which is fabricated near a simultaneously fabricated workpiece, and the diffracted electromagnetic radiation is analyzed. Insight to whether or not the workpiece was fabricated correctly is obtained from analysis of the diffracted beam, (ie. a structured sample) as opposed to investigating the workpiece directly. For insight at this point, it is noted that the present invention does not require use of a structured diffraction producing system to determine characteristics of a sample under investigation, but rather applies electromagnetic radiation to directly investigate samples.